Thread trimming mechanism for sewing machines



R. J. Ross 3,

THREAD TRIMMING MECHANISM FOR SEWING MACHINES June 4, 1968 4 Sheets-Sheet 1 Filed July 5, 1966 INVENTOR. Roger J. Ross R. J. ROSS 3,386,402

THREAD TRIMMING MECHANISM FOR SEWING MACHINES June 4, 1968 4 Sheets-Sheet 2 Filed July 5, 1966 ms T8 N0 H W N m Ofm Q. m r I e A g m QM.

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vz-mz THREAD TRIMMiNG MECHANISM FOR SEWING MACHINES Filed July 5. 1966 R. J. RQSS June 4, 1968 4 Sheets-Sheet 3 Fig. 5.

INVENTOR. Roger J. Ross WITNESS:

June 4, 1968 R. J. ROSS 3,386,402

THREAD TRIMMING MECHANISM FOR SEWING MACHINES Filed July 5, 1966 4 Sheets sheet 4 CONTROL SY M \p. v J M 1 S L-l 7 INVENTOR. (60) Roger J. Ross WITNESS: /Q'w- \fcleefy/ I fie -M ATTQRNEY United States Patent 3,386,402 THREAD TRIMMING MECHANISM FOR SEWING MACHINES Roger J. Ross, Dover, N.J., assignor to The Singer Company, New York, N.Y., a corporation of New Jersey Filed July 5, 1966, Ser. No. 562,576 Claims. (Cl. 112-252) This invention relates to thread trimming mechanism for lock stitch sewing machines, and more particularly, to a mechanism for trimming both the needle and bobbin threads, closely adjacent to the work and for providing sufficient lengths of thread to the bobbin and to the needle after trimming so that stitching on a succeeding seam may proceed.

It is an object of this invention to provide a novel and effective thread trimming mechanism which may be applied completely beneath the bed of a sewing machine and which does not require alteration or modification of the stitch forming instrumentalities. The trimming mechanism of this invention may thus be applied to any conventional lock stitch machine without adversely influencing the stitching characteristics. Furthermore, the presence of the trimming mechanism of this invention does not interfere with any fittings, work guides or other attachments to the sewing machine.

Another object of this invention is to provide a thread trimming mechanism adapted to cooperate in a novel and advantageous manner with a programming device such as a needle positioner for a non-cyclic sewing machine.

Trimming mechanisms for the sewing threads are most highly developed in the prior art in association with sewing machines which are cyclic in operation such as buttonhole machines or tackers. Included as part of such cyclic sewing machines for purposes other than thread trimming, are stop motion devices and programming devices such as cams or the like. When thread trimming mechanisms have been heretofore incorporated in cyclic sewing machines, therefore, they have been operatively interconnected with the sewing machine stop motion and programming devices with the result that all mechanisms associated with the thread trimmers including the operating mechanism and controls therefor are carried by the sewing machine frame.

There are, furthermore, known in the prior art thread trimming devices for sewing machines which are not cyclic in operation. Here also it is conventional for the operating mechanism and controls for the trimmers to be carried by the sewing machine frame. The elements of a thread trimming mechanism which engage and manipulate the threads constitute only a small proportion of the total structure and cost of the entire trimming mechanism, with a far higher proportion being accounted for in the actuating and control mechanisms for the trimmer. The disadvantages of the known thread trimming mechanisms are not only that the entire cost of a trimming mechanism must be included in the cost of each individual sewing machine to which it is applied but also that the already limited space available in a sewing machine frame is burdened by inclusion of the entire trimming mechanism.

The present invention obviates these disadvantages of the known trimming mechanisms by the provision of a thread trimming mechanism in which only those elements which engage and manipulate the threads need be carried by the sewing machine. The actuating mechanism for the trimmer as well as the control means therefore may be associated with the power table on which the sewing machine is exchangeably supported. As a result, each sewing machine need only be burdened with a minor portion of the structure and cost of the trimmer and the sewing machine support which can accommodate inter- "ice changeably any one of a plurality of sewing machines is fitted with the actuating and control mechanism for the thread trimmer.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.

FIG. 1 is a fragmentary perspective view of a rotary hook, a needle and a needle thread take-up member associated with thread cutting and thread catching tools, in positions required immediately prior to the threadcatching and thread-trimming operations in accordance with this invention;

FIG. 2 is a fragmentary perspective view showing the mechanism illustrated in FIG. 1 with the parts located in the positions to which they travel immediately subsequent to thread-catching and thread-trimming;

FIG. 3 is a left elevation of a sewing machine, including the mechanism shown in FIG. 1 and associated elements provided for operation thereof;

FIG. 4 is a bottom perspective view of most of the elements of the thread-trimming and thread-catching mechanism shown in FIG. 3, removed from the sewing machine;

FIG. 5 is a fragmentary bottom plan view of the machine shown in FIG. 3;

FIG. 6 is a cross sectional view taken substantially along line 6-6 of FIG. 5;

FIG. 7 is a schematic diagram of a sewing machine including a needle positioning control system for a trimming device in accordance with this invention, and

FIG. 8 is an electrical schematic diagram of the control system shown in FIG. 7.

Referring to FIG. 1, a rotary hook 10 is secured to the bed shaft 11 of a lock stitch sewing machine. Operation of such a rotary hook is described in the US. patent of Habedonk et al., No. 3,074,367, I an. 22, 1963. Iournaled within the rotary hook 10 is a bobbin carrying case 12 which is prevented from rotating by a rotation restraining finger 13 secured to the bed of the sewing machine and inserted into a rotation restraining notch 14 in the bobbin carrying case 12. The rotary hook includes a hook beak 15 which partakes of two revolutions in cooperation with each vertical reciprocation of a needle 16 to concatenate threads into lock stitches. The conventional thread takeup member 17 cooperates to manipulate the needle thread in the conventional manner.

A thread catching finger 18 having a thread catching hook 19 on one end thereof is shown in FIG. I inserted into a thread catching aperture 20 in the bobbin carrying case 12. The bobbin carrying case 12 is identical to standard cases with the exception of provision of the thread catching aperture 20 which is provided to receive the thread catching hook 19.

As shown in FIG. 1, the thread catching hook 19 is positioned in the thread catching aperture 20 in such manner that the bobbin thread B and the needle loop L have been pulled against it by the counter-clockwise rotation of the hook beak 15, so that upon retraction of the thread catching finger 18, the thread catching hook 19 draws the bobbin thread B and the needle loop L to the left, away from the rotary hook 10. However, the work limb N of the needle thread and the bobbin thread B passing to the work represented by the line of stitches S are drawn behind the rotation restraining finger 13, whereas the needle limb N of the needle thread is drawn by the hook beak 15 into a position finally overlying the rotation restraining finger 13, as shown in FIG. 2. The thread catching hook 19 is preferably inserted into the thread catching aperture 20 when the needle is in its lower dead center position, approximately at the time when the hook beak is first engaging a needle loop L. As the hook beak 15 rotates, the needle loop is pulled thereby against the thread catching finger 18, and the bobbin thread B is positioned in a slot 9 in the bobbin carrying case 12, which slot 9 is aligned with the thread catching aperture and the path traversed by the thread catching finger 18 and hook 19 during a stroke thereof.

After the thread limbs have been caught and drawn outwardly by the thread catching hook 19 to a length permitting cutting of sufficient lengths of needle and bobbin threads for resumption of sewing following trimming without manipulation, a knife 41 can be drawn across the work limb N of the needle thread and the bobbin thread B. Because the knife travels below the needle limb N,,, that limb will not be trimmed and will remain long enough for commencement of the next sewing operation. When the cutting stroke occurs preferably at top dead center of the needle, the needle thread take-up member 17 will be raised, in the conventional manner, for tightening the last stitch S and providing tension on the threads. Provision of adequate tension permits employing a single blade 41 operative without employing an opposing blade, i.e., without a scissors action, to trim the limbs of thread if they are struck by the blade 41 with con siderable impact. Tension also assures that the needle limb N will not be cut because it is retained by the thread catching hook 19, the rotation restraining finger 13 and the wall of a needle aperture '54 in a throat plate 39 (see FIG. 2) sufiiciently distant from the knife 41.

Referring to FIGS. 3 and 4, the thread-catching finger 18 is secured at the end opposite its thread-catching hook 19 to a clamping arm affixed to a guide rod 23 slidably supported in a hole through a supporting bracket 21 secured to one column or foot 38 which depends from the sewing machine bed 33 and to a supporting bar 37 secured to another column or foot 38. The guide rod 23 has a longitudinal alignment slot 26 retained in alignment by an alignment pin 25 inserted through and secured to the supporting bracket 21, so that the thread-catching finger 18 will be guided along the same longitudinal path by the guide rod 23. The guide rod 23 may be driven into the hole through the supporting bracket by means of a first solenoid 60, having a plunger 61 aligned to strike the outer end of the guide rod 23 as illustrated in FIGS. 6 and 7.

The guide rod is hollowed from its outer end to the opposite end of the alignment slot 26 for receiving a coil spring 24 adapted to engage alignment pin 25 at one end and a set screw 62 at its opposite end. Set screw 62 is secured concentrically in the outer end of the guide rod 23 by means of threads therein. Coil spring 24 urges the guide rod outwardly.

As the thread catching hook 19 must remain inserted within the thread catching notch 20 until the needle loop L as been drawn around the thread catching finger 18, a latch is provided for temporarily holding the guide rod inserted within the supporting bracket 21. The latching mechanism comprises a latch notch 27 formed in the guide rod on the portion thereof which will extend outside the opposite end of the supporting bar 21 and a latch lever 28 pivoted on a latch lever pivot pin 36 is secured to the supporting bracket 21 and supporting bar 37. A latch spring 29 housed in confronting holes in the supporting bracket 21 and the latch lever 28 biases the opposite end of the latch lever into engagement with the portion of the guide rod 23 extending outside the adjacent end of the hole through the supporting bracket. Thus, the latch lever 28 will be forced into the latch notch 27 by the latch spring 29 when the guide rod 23 is driven inwardly by the plunger 61 of the first solenoid. 60. The latch lever 28 is pivoted in a space defined between a recess in the supporting bracket 21 and one side of supporting bar 37.

Referring to FIG. 5, the sewing machine includes a conventional drop feed mechanism such as that shown in the US. patent of Van Ness, No. 2,848,694, to which reference may be had. The work feeding mechanism includes a work feed dog which is raised into engagement with work fabric being sewn after each upstroke of the needle by a feed lifting rock shaft 32. Since it is on the upstroke of the needle that the thread catching finger must be removed from the thread catching notch 20, the feed lifting rock shaft 32 has a latch-releasing ear 31 secured thereto to engage the end of a sliding latch-releasing link 30 pivotally secured at its opposite end to the opposite end of latch lever 28. The latch releasing e'ar 31 forces the latch lever 28 against latch spring 29 and releases engagement of the latch lever 28 within the latch notch 27 in the guide rod 23. Thus, the spring-biased guide rod 23 and the thread-carrying finger 18 will be driven outwardly by spring 24, carrying the threads therewith.

Subsequently, after the needle 16 has been drawn out of the needle aperture 54 to top dead center, and the needle-thread take-up member 17 is fully raised, the knife 41 may be operated most effectively.

The knife 41 is secured to a knife-holder arm 43 extending from a knife-holder ring 42 journalled on the outer surface of the bearing 53 for the bed shaft 11. The knifeholder ring 42 and the bearing 53 are concentric with the bed shaft 11. The knife-holder ring 42 is secured against lateral motion by a forked retaining spring 45 secured to one of the bed-supporting columns 38.

Extending from the knife holder ring 42 is an arm having a knife-holder pin 44 extending therefrom into engagement with a slot 52 in a turned tab 51 formed on one end of a bell-crank lever 46 pivotally secured to the supporting bracket 21 by a pivot screw 48 and having a turned car 49 at its opposite end. A second solenoid 63 as illustrated in FIGS. 5, 6 and 7 has a plunger 64 aligned to strike the ear 49, thereby pivoting the bell-crank lever 46 to push the knife-holder pin 44, thereby turning the knife-holder ring 42, arm 43 and the knife 41 to cut the threads. A return spring 59 secured to the bell-crank lever 46 and the supporting bracket 21 returns the bell-crank lever 46 and the knife 41 and its holder to normal position upon retraction of the plunger 64 of the second solenoid 63.

As illustrated in FIGS. 5, 6 and 7, the sewing machine to which this invention is illustrated as being applied in the accompanying drawings is of the type adapted to be supported in a cut-out 5-5 of a power table top 56 which may be floor supported by legs 57. While the thread catching member and the thread trimming mechanism hereinbefore described are supported on the sewing machine frame, the solenoids 60 and 63 may be carried by the power table top 56. Moreover, the control mechanism for operating the solenoids 60 and 63 in correlation with a sewing machine control programmer such as a needle positioner as will hereinafter be described may also be carried by the power table. As a consequence, the sewing machine frame need not be burdened with the trimmer operating or control means and critical space in the sewing machine frame is spared. It is also an advantage that individual sewing machines may be exchanged in the power table each cooperating with the one set of trimmer actuating solenoids and the control mechanism on the power table.

As both the thread-catching and the trimming mechanisms are adapted to be actuated by solenoids, this thread-trimming system is especially well suited for operation in response to programmed control. In particular, needle positioners and cooperating control systems can and have been successfully employed to control operation of this type of thread trimmer.

In FIG. 4, substantially all of the additional parts required to be added to a conventional sewing machine for the instant trimming and thread-catching system are shown with the exception of the latch releasing ear 31, and the solenoids and 63. The sole modifications required to be made to a conventional sewing machine to accept this trimming mechanism other than tapping or providing mounting holes, comprise smoothing of the rotation restraining finger 13 and providing the threadcatching aperture 20 in the bobbin carrying case 12.

In the operation of the thread-catching and trimming mechanism of this invention, three steps are required to be performed. At or near bottom dead center position of needle reciprocation, the thread catcher must be shifted into the thread-catching aperture 20 as by atcuation of the first solenoid 60. Thereafter, the needle must be reciprocated toward top dead center position during which motion, the thread-catching finger will be unlatched and in returning to the at-rest position, will draw the thread loops out of the rotary hook. As a final step, the knife must be operated as by actuation of the second solenoid 63.

This trimmer can be operated in several fashions, including employing manually operated switches, when the sewing machine is properly positioned manually or by an independent needle positioner.

However, the trimmer described herein is particularly well adapted to be employed in combination with a needle positioner of the variety described in US. Larys et al. Patent No. 2,942,564 which employs an auxiliary motor and a timer and clutch which can be secured in place of the usual balance wheel and synchronized with reciprocation of the needle bar of the sewing machine.

As the Larys et al. patent describes a needle positioner without making any reference to a trimmer, and because the present trimmer is adapted to operate in accordance with the above-described sequence, employment of a control unit for coordination of the system is desirable. It is especially important that the knife operate only when the needle has been removed from the needle aperture and that the thread catching finger be inserted after the needle has been lowered.

In FIG. 7, units of a control system adapted to operate a trimmer in accordance with this invention are shown generally to indicate how they can be employed on a sewing machine. Timing of the trimming device is effected by employing a needle positioning device basically of the variety disclosed in the above Larys et al. patent. The needle positioning device includes a clutch-and-timer unit secured in place of the conventional balance wheel of a sewing machine head 75. The details of construction of such a unit are disclosed in the above Larys et al. patent. Basically, however, the clutch is double acting and is biased to connect the transmitter belt B1 driven by a conventional clutch-brake transmitter M1 to the arm shaft of the sewing machine. Operation of a clutch solenoid SOL-3 (FIG. 8) in the clutch-and-timer unit 70 drives the clutch therein into a position connecting an auxiliary belt B2 driven by an auxiliary motor M2 to the arm shaft. The auxiliary motor M2 is operable at a lower speed which permits slow and accurate needle positioning. A normally-closed control switch S3 is secured to the transmitter operating lever 78 of the transmitter M1. Lever 78 is employed for controlling the clutch and brake thereof. The control switch S3 will be opened to remove power from the elements of a control system 74 when the transmitter-operating lever 78 is lowered by depressing the treadle 77. Lowering of the transmitter-operating lever releases the brake and engages the clutch of the transmitter M1 to drive the transmitter belt B1.

When the operator raises the lower link of a pitman 76 connecting the treadle 77 to the transmitter operating lever 78 by heeling the treadle 77, a normally-open heel switch S1 will be closed to cause the control system 74 to position the needle 16 in the needle aperture 54, i.e., down. Then the transmitter M1 will be in 6 braked condition and the system will be prepared for trimming.

If it is desired to sew additional stitches prior to trimming, a toe switch S5 secured to the treadle 77 can be closed. This causes the control system '74 to operate a solenoid SOL-3 in the clutch-and-timer unit 70 to connect the auxiliary belt B-2 to the arm shaft. The control switch S3 will be closed, because the transmitter-operating lever 78 will be in its at rest position, and accordingly the auxiliary motor M2 will be powered. In this way, the toe switch S5 can drive the sewing machine at low speed for as many needle strokes as the operator desires.

Then the system may be prepared for trimming by heeling the treadle 77 thereby closing the heel switch S1 and consequently, positioning the needle 16 down. Subsequent operation of a knee switch S2 by a knee pedal will close contacts causing the thread catching finger 18 to be driven into position by solenoid 60, simultaneously raising the needle 16 to the up position and releasing the latch holding the thread catching finger as described above, and causing the control system to actuate the thread cutting solenoid 63 to operate the knife 41 when the timer in the clutch and timer unit 70 indicates that the needle has been raised to the up position.

Operation of the trimmer solenoid 63 will cause a solenoid switch S6 to be closed, thereby preventing further low-speed operation by the slow-speed toe switch S5.

Further aspects of operation of the needle positioner and control system are described below with reference to FIG. 8 which is a schematic diagram of the pertinent portions of the electrical system of this invention.

An alternating current power supply AC is connected through a power switch S4 and the normally-closed contacts of the control switch S3 to a full-wave rectifier R. The control switch S3 is opened by the clutch arm when the treadle 77 is depressed by the toe of the operator to disconnect power from the circuit, i.e., when the sewing machine is being operated at full speed. The fullwave rectifier R supplies power across the lines A-B.

When the treadle 77 is heeled by the operator, contacts of the heel switch S1 are closed to pass current through a clutch solenoid SOL-3 in the clutch and timer unit 70 which drives the clutch into position to connect the arm shaft to the auxiliary motor M2 for the purpose of lowering the needle to lower dead center position. Current passes from line A to line B through contacts of the heel switch S1, normally-closed contacts Rl-CZ of a knee relay R1 and the lower timing points S7 of the timer 71 which is operated by a timing cam 72 having a projection 73 broad enough to provide appropriate positioning by holding the points open long enough to assure full braking. The clutch solenoid SOL-3 for connecting the clutch in the clutch and timer unit 70 to the auxiliary belt B-2 of the auxiliary motor M2 is connected by a first slip ring to lower timing points S7 and by a second slip ring 81 through normally-closed clutch control contacts R2-C6 of an end-of-cycle relay R2 to line B.

When the sewing machine reaches its lower dead-center needle position, the timing cam 72 opens the lower timing points S7 thereby releasing the clutch of the unit 70 to its normal position in which the arm shaft is reconnected to the transmitter belt B1. The transmitter M1 will have been braked previously when the treadle 77 was positioned in its normal at rest position (or was heeled by the operator). Thus, the brake of the transmitter M1 will then be connected to brake the arm shaft of the sewing machine. If desired, a toe switch S5 can be operated to operate the sewing machine at a low speed to end the line of stitches precisely where desired. Switch S5 supplies power from line A to the clutch solenoid SOL-3. Then when S5 is released contacts S7 will reposition the needle. Then the operator may operate the knee switch S2 to close its normally-open contacts, thereby connecting the coil of the knee relay R1 across lines A and B to close three sets of contacts Rl-Cl, Rl-C3 and Rl-C4 and open one set of down control contacts Rl-CZ. The normally-open holding contacts Rl-Cl hold the knee relay R1 in operation during the remainder of the trimming operation. Normally-closed down control contacts Rl-CZ open, thereby disconnecting the circuit through the lower timing points S7 of the timer, to prevent operation of the machine beyond top dead center after the needle 16 has been positioned down.

Normally-open up control contacts R1-C3 are closed by the knee relay R1 thereby supplying power to the clutch solenoid SOL3 through the upper timing points 8-8 which will now be closed because the needle 16 is down and timing cam 72 will be in a corresponding position holding the lower timing points S7 open. Thus, the needle 16 will be driven relatively slowly out of the needle aperture 54.

Simultaneously with the above, the knee relay R1 closes the cutting control contacts R1-C4 to power a solenoid control relay R3 to reverse a single-pole double-throw thread-catching switch R3-C8 to connect a charged capacitor CAP-2 across the finger solenoid SOL-2 or 60 which supplies an impulse to SOL-2 to drive the thread-catching finger 18 into the finger aperture 20 in the bobbin-carrying case 12. The capacitor CAP-2 will have been charged previously by connection through the blade of the thread catching switch R3-C8 and the pole connected to line B (one end of both capacitor CAP-2 and finger solenoid SOL-2 is connected to line A), across lines A and B. As described above the finger is latched and then released in timed relationship with the position of the needle.

A second single-pole, double-throw trimmer switch R3C7 is also operated to connect one end of a capacitor CAP-1 (connected between a cutting control contact R1-C4 and the blade of the trimmer switch R3C7) to line B, the other end thereof bein connected to line A through the cutting control contacts Rl-Cd, upper timing points S3 and a pair of up control contacts Rll-C3. Thus, capacitor CAP1 will have been charged for operating the thread-cutting solenoid SOL-1, when the blade of the thread cutting switch R3-C7 is subsequently returned to its normal position connecting the thread-cutting solenoid SOL1 and capacitor CAP-1 in parallel, after the upper timing points S8 have opened.

The sewing machine will be driven until the upper timing points S8 of the timer 71 open, at top-dead-center needle position, thereby disconnecting power from the solenoid control relay R3 to return the trimmer switch R3C7 to its normal position with the capacitor CAP-1 connected across the thread cutting solenoid SOL-1 (63) thereby operating the thread-cutting solenoid SOL-1 (63) by an impulse of current from the capacitor CAP-1.

The solenoid switch S6 is momentarily closed by the trimmer actuating solenoid SOL-1 (63) as its plunger reciprocates while actuat ng the trimmer linkage. Switch S6 connects line B to the coil of an end-of-cycle relay R2 which closes a pair of normally-open holding contacts R2-C5 in series with the end-of-cycle relay R2 across lines A and B. The end-of-cycle relay R2 is provided to open normally-closed clutch control contacts R2C6 Which disconnect the slip rings 80, 81 from line B, thereby preventing repeated positioning of the machine, should the operator attempt to operate the machine at slow speed subsequent to trimming by means of toe switch S and heel switch S3. This is desirable because otherwise new stitches would be sewn and repeated operation of the trimmer would be required, thereby slowing production. Thus, accidental operation of the toe switch S5 after trimming will not tend to slow production.

It will be understood that the system can be manufactured without the toe switch S5 and that the end of cycle relay R2 and the solenoid switch S6 can be eliminated from the circuit without affecting the operation of the trimming device of this invention. It is also interesting to note that the toe switch S5 is not connected in series with the timing points, and accordingly, it is not employed as a needle positioning control. It is simply an actuator for the clutch in the unit for temporarily connecting the auxiliary motor M2 to the arm shaft.

If by mistake, the knee switch S2 were operated before the heel switch 81 had been actuated, no problem would be encountered, because the trimmer would operate only after the up timing points S8 had opened removing power from the solenoid control relay R3 and thus providing an impulse of power from capacitor CAP-1 to the trimmer solenoid SOL-1. The down timing points S7 would be excluded from the circuit by the down control contacts Rl-CZ which would prevent stopping of the machine with the needle down.

Thus the needle would not be in the needle aperture, i.e., in a position to be struck by the knife. Under such circumstances, the treadle would have to be depressed to open the control switch S3, or switch S4 could be opened momentarily thereby shutting off power to the circuit and therefore reopening the holding contacts R1-C1 of the then deenergized knee relay R1 in order to permit operation through the trimming cycle in the proper sequence.

In any event, the treadle must be depressed in order to return the control system to its initial condition after the heel switch S2 has been closed, thereby reopening the normally-open holding contacts Rl-Cl.

Having thus set forth the nature of this invention, What is claimed herein is:

1. A device for trimming the sewing threads of. a lock stitch sewing machine having a reciprocating thread carrying needle, a loop taker including a thread carrying bobbin, drive means interconnecting said needle and loop taker for movement in timed relation in the formation of lock stitches, motor means operatively connected to said drive means, and a needle positioning device operatively connected to said drive means, first operator influenced means for at will interrupting operation of said drive means by said motor means, second operator influenced means effective upon interruption of operation of said drive means by said motor means for operating said needle positioning 'device to drive said needle to a preselected position, said thread trimming device comprising a thread catching element shiftably supported on said sewing machine for movement relatively to said loop taker to engage and distend loops of thread from both said needle and said bobbin, a thread cutter shiftably supported on said sewing machine for movement relatively to said loop taker to sever at least one limb of each of said needle and bobbin thread loops distended by said thread catching element, actuating means for said thread catching element and for said thread cutter, third operator influenced means for operating said needle positioning device to drive said needle beyond said preselected position subsequent to actuation of said second operator infiuenced means and for initiating operation of said actuating means to shift said thread catching element and said thread cutter in seriatim, and interlock means rendering said actuating means ineffective to shift said thread catching element and said thread cutter except in respective predetermined positions of reciprocation of said needle subsequent to operation of said needle positioning device in response to operation of said second operator influenced means.

2. A thread trimming device for a sewing machine as set forth in claim 1 including a power table in which said sewing machine is adapted to be removably supported, in which said actuating means for said thread catching element and for said thread cutter are carried by said power table.

3. A thread trimming device for a sewing machine as set forth in claim 1 in which individual actuating means are provided for said thread catching element and for said thread cutter and in which said interlock means renders each of said individual actuating means effective in a different position of reciprocation of said needle in response to operation of said needle by said needle positioning device beyond said preselected position.

4. A thread trimming device for a sewing machine as set forth in claim 3 in which said interlock means renders effective said actuating means for said thread catching member only while said needle is reciprocated by said needle positioner into a work penetrating position which comprises said preselected position, and said interlock means renders effective said actuating means for said thread cutter only after the next subsequent elevation of said needle by said needle positioning device after operation of said actuating means for said thread catching element.

5. A thread trimming device for a sewing machine as set forth in claim 4 in which said thread-catching element is secured to a member spaced substantially from said loop taker and movable from a biased position into a position of proximity to said loop taker in the path of said needle thread and said :bob-bin thread, latch means constraining said thread catching element in said position of proximity for a predetermined angle of rotation of said loop taker, and means operable by said drive means for releasing said latch means when said needle reaches a said predetermined position, said latch release means being timed to follow engagement of said thread catching element with said thread loops for the purpose of distending said thread loops, said needle positioning device operating a switch upon elevation of said needle, and said switch operatively connected with said interlocking means to enable said actuating means to operate said thread cutter. 7

6. In a lock stitch sewing machine having a vertically recip-rocatory thread carrying needle, a needle thread take up mechanism efliective to draw the needle thread taut during upstroke of the needle, a loop taker operatively connected with said needle and including a thread carrying bobbin, drive means for said needle, loop taker and take up mechanism, operator influenced means for at will interrupting said drive means and a needle positioning device effective to position said needle selectively either up or down, a trimming device for both the needle and bobbin threads comprising a thread catching element shiftably supported on said sewing machine for movement relatively to said loop taker into and out of the path of needle and bobbin threads thereon, a thread cutter shiftably supported on said sewing machine for movement relatively to said loop taker, actuating means for operating said thread trimming device and said needle ositioner in concert and including operator influenced means for shifting said thread catching element into a shifted position in the path of said needle and bobbin threads on said loop taker only when said needle is positioned down by said needle positioner, detaining means for detaining said thread catching element in said shifted position, operator influenced means for operating said needle positioner to raise said needle, and means rendered effective by said operationof said needle positioner to raise said needle, to release said thread catching element detaining means and to actuate said thread cutter in seriatim.

7. A sewing machine thread trimming device as set forth in claim 6 in which said actuating means for operating said thread trimming device and said needle positioner in concert is operated electrically and includes solenoids for operating said thread catching element and said thread cutter.

8. A sewing machine thread trimming device as set forth in claim 7 including a power table in which said sewing machine is adapted to be supported, in which said actuating mechanism including said solenoids for operating said thread catching element and said thread cutter are carried by said power table, and in which said thread catching element and said thread cutter are arranged on said sewing machine for operation by said power ta-ble supported solenoids when said sewing machine is supported on said power table.

9. A sewing machine thread trimming device as set forth in claim 7 in which said needle positioning device controls electrical interlock circuitry included in said actuating means, whereby said needle positioner provides an electrical output shifting said interlock circuitry when the needle is positioned down to permit operation of said solenoids, and further interlock circuitry connected with a said solenoid for operating said thread cutter, said further circuitry including a switch responsive to mechanism synchronized with said needle to indicate elevation of said needle above the level of said thread cutter.

10. A sewing machine thread trimming device as set forth in claim 9, wherein adjacent said solenoid for operating said thread cutter is a second switch for disabling said needle positioning device connected to additional interlock circuitry, which second switch is operatively connected to be operated by said solenoid for operating said thread cutter upon actuation thereof, said additional interlock circuitry remaining operative to disable said needle positioning device until interruption of said drive means is terminated.

References Cited UNITED STATES PATENTS 1,272,066 7/1918 Lyons 112252 1,298,786 4/ 1919 Ray 112252 1,938,128 12/1933 Wood 112-252 2,942,564 6/1960 Larys 112-219 3,308,776 3/1967 Ivanko 112-252 X HERBERT F. ROSS, Primary Examiner. 

6. IN A LOCK STITCH SEWING MACHINE HAVING A VERTICALLY RECIPROCATORY THREAD CARRYING NEEDLE, A NEEDLE THREAD TAKE UP MECHANISM EFFECTIVE TO DRAW THE NEEDLE THREAD TAUT DURING UPSTROKE OF THE NEEDLE, A LOOP TAKER OPERATIVELY CONNECTED WITH SAID NEEDLE AND INCLUDING A THREAD CARRYING BOBBIN, DRIVE MEANS FOR SAID NEEDLE LOOP TAKER AND TAKE UP MECHANISM, OPERATOR INFLUENCED MEANS FOR AT WILL INTERRUPTING SAID DRIVE MEANS AND A NEEDLE POSITIONING DEVICE EFFECTIVE TO POSITION SAID NEEDLE SELECTIVELY EITHER UP OR DOWN, A TRIMMING DEVICE FOR BOTH THE NEEDLE AND BOBBIN THREADS COMPRISING A THREAD CATCHING ELEMENT SHIFTABLY SUPPORTED ON SAID SEWING MACHINE FOR MOVEMENT RELATIVELY TO SAID LOOP TAKER INTO AND OUT OF THE PATH OF NEEDLE AND BOBBIN THREADS THEREON, A THREAD CUTTER SHIFTABLY SUPPORTED ON SAID SEWING MACHINE FOR MOVEMENT RELATIVELY TO SAID LOOP TAKER, ACTUATING MEANS FOR OPERATING SAID THREAD TRIMMING DEVICE AND SAID NEEDLE POSITIONER IN CONCERT AND INCLUDING OPERATOR INFLUENCED MEANS FOR 